1. Field of the Invention
This invention relates to a method of laying a road, and more precisely to a method of laying a road characterized by the use of a specific water repellent agent to reduce the road damage due to a frozen roadbed.
2. The Prior Art
A frozen roadbed is a natural phenomenon generally observed in winter and/or in cold regions. In general, when the temperature of the roadbed drops below 0.degree. C., the roadbed freezes because water in the roadbed forms ice or because water which has risen from the roadbed to the earth surface via the capillary phenomenon forms ice.
As described above, the extent of the occurrence of frozen roadbeds and frost columns is affected by the conditions of the ground foundation which contains the water and also by weather conditions. An example of roadbeds which tend to cause freezing and frost columns is a clay or silt layer with a smaller particle size which has a large amount of water retained in the roadbed (suspending water) and also has a strong capillary attraction.
When a roadbed freezes, since water in the roadbed freezes to form an ice layer(s), its volume expands and the roadbed swells to lift up the road surface or the roadbed surface expands to cause unevenness.
When only the water existing in the roadbed freezes, the volume expansion is about 9% and lift-up of the road surface is limited. However, if water is supplied to the roadbed from underground water via the capillary phenomenon, then the ice layer grows to create a larger expansion force, thus causing greater road damage due to the lift-up of the road surface and/or expansion of the roadbed surface.
In particular for paved roads whose roadbeds are paved with concrete, asphalt and such, serious damage to the road surface, such as peeling and cracking of the paved surface, will occur. Also, if a roadbed is kept frozen for a long time after the ice near the earth surface on the frozen roadbed has thawed, then water from melted ice, rain and such does not penetrate into the earth and stays on the road surface, sometimes causing bad road conditions.
Furthermore, when spring comes and melts the ice, increasing the water content in the roadbed, the roadbed may become soft and weak, and lose the strength necessary to support the road surface, thus causing road breakage due to the traffic load.
Conventionally, the following methods have been adopted to prevent freezing in roadbeds:
(1) Lowering the underground water level PA1 (2) Raising the road surface PA1 (3) Blocking capillary water by establishing a layer(s) consisting of a low capillary-rise material(s) such as a sand layer, a gravel layer, a crushed stone layer or a mixture of these, or a non-water-permeable layer(s) such as asphalt paper or an asphalt-tar layer at an adequate depth in the roadbed PA1 (4) Replacing the soil in the roadbed with a material which does not freeze easily, such as gravel, crushed stone or sand PA1 (5) Providing a thermal insulation layer(s) near the road surface.
However, the conventional methods such as those described above have not been sufficiently effective countermeasures against frozen roadbeds. That is, methods such as lowering the underground water level or raising the earth surface level are not necessarily easy solutions. For example, in order to lower the underground water level, it is necessary to provide drain pipes, blind ditches, etc., and there are problems in that the construction period is very long and costs are very high.
Also, it is impossible to completely prevent freezing of the roadbed solely by a layer consisting of a low capillary-rise material(s) such as a sand layer, a gravel layer or a crushed stone layer, and the sand layer has to be particularly thick to have a significant effect.
Also, a non-water-permeable layer has the shortcomings of poor water drainage because water on the road surface is not absorbed into the roadbed, thus causing soft and weak road surfaces. Also, methods such as replacing the roadbed with a material(s) which does not freeze easily, or providing a thermal insulation layer(s) near the road surface lead to high costs, and are not necessarily realistic solutions for roads in general.